php ternary operator formatting

Question

This works:

<input type="text" name="foo" value="<?php echo isset($_POST['foo']) ? $_POST['foo'] : '' ?>"/>

This does not:

echo('<input type="text" name="foo" value="'.isset($_POST['foo']) ? $_POST['foo'] : ''.'"/>');

Notice: Undefined index: foo in /srv/www/form.php on line 15

Thanks for any help.

Answer 1

将表达式放在括号中：

echo('<input type="text" name="foo" value="'. (isset($_POST['foo']) ? $_POST['foo'] : '') .'"/>');

Answer 2

PHP's operator precedence rules make it evaluate your second example as follows:

echo(
  ('<input type="text" name="foo" value="'.isset($_POST['foo']))
    ? $_POST['foo']
    : (''.'"/>')
);

That doesn't make a lot of sense in several ways. And since the result of isset() is essentially disregarded, this always ends up just trying to print $_POST['foo'] . And that results in a notice when it's not set, of course.

Add parentheses around the actual ternary expression. Ie

(isset($_POST['foo']) ? $_POST['foo'] : '')

Answer 3

IMHO, parenthesis (as suggested by zerkms) makes code unreadable.

Instead, think something like this:

$value = isset($_POST['foo']) ? $_POST['foo'] : '';
echo '<input type="text" name="foo" value="'. $value .'"/>';